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Chlorofluorocarbons (CFCs) used to be in everything from hairsprays to refrigerators to air conditioning units. They contain the molecules chlorine and bromine, which were destroying the atmosphere before US researcher Susan Solomon discovered their effect in 1986.

The discovery led to a global ban under the Montreal Protocol in 1987. Since this, it appears the situation has been slowly improving.

Researchers at MIT compared the ‘thinning’ between 2000 and last year. They found that the hole above Antarctica is now around four million sq. km – roughly the size of India but smaller than before.

Professor Solomon and her colleagues made their discovery while conducting detailed measurements, via weather balloons, satellites and model simulations, of the amount of ozone in the stratosphere between 2000 and 2015.

Speaking to the BBC World Service’s Science in Action programme, Prof. Solomon said, "even though we phased out the production of CFCs in all countries including India and China around the year 2000, there's still a lot of chlorine left in the atmosphere".

She went on to say that this will take 50 to 100 years to decay, predicting that the recovery will not be complete till at least 2050 or 2060.

More work needs to be done

Most countries have now instituted f-gas phase-down strategies, which should help to make sure this healing continues in the future.

Natural refrigerants ammonia, CO2, hydrocarbons, water and air do not deplete the ozone layer and offer an alternative to f-gases in HVAC&R applications worldwide.